Jeff Brett on fri 28 jul 00
Tom,
We've used a catenary arch at the college where I work for a number
of years. It has a few hot spots but nothing that careful kiln
loading and firing couldn't remedy. The top did not tend to vary more
than a half cone in a good firing. We found that a longer firing
would also tend to even things out (8 hours plus). Sometimes our
students liked to achieve the fastest firing on record (so far 5
hours) but it was always very uneven.
We built the rear wall part inside and outside the arch. The
expansion doesn't seem to affect it much and having part of the wall
outside the arch and overlapping helps seal it.
We've always bricked in the door and it fits inside and outside the
arch like the rear wall. A bit of a challenge when we initial fit it
together but it is carefully numbered with red iron oxide. It needs
replacement every few years which isn't bad for a college art
department.
Our catenary is actually two arches one inside the other. It has a
complete inside arch of soft insulating (no mortar). The outer arch
has hard brick part way up. The only area we mortared was the hard
brick in the outside arch. The top of the outside arch is 2 layers of
ceramics blanket with cement fondue over. The cap moves easily when
the arch expands during a firing and settles down nicely as it cools.
The biggest disadvantage I see to a catenary arch is the loss of
width at the top. We'll soon replace ours with a sprung arch kiln.
I'll miss the elegance of our catenary. If you'd like a few pictures
to ilIustrate my description i'd be glad to email them your way. Let
me know.
....Jeff
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